I have had this system for five years or so and its never given anything much in the way of problems but now.........With the changeover switch set to backwash/waste/rinse or anything but filter everything's fine but when its set on filter the pressure rises to 3 bar (its normally around the 1 bar mark) and water starts to leak back through the filter basket on the pump no doubt due to the extremely high pressure.I would assume that the intake to the sand filter has, somehow or other, become blocked; I've had the top off the sand filter and felt around with my hands but the sand moves easily and isn't 'caked'. It would be a nightmare to attempt to dis-assemble the intake pipes to the filter and, in any event, cannot see how anything of substance could have got past the filter basket on the pump to have blocked the sand filter intake.Anyone any ideas before I take a saw to the pipes which I'm going to have to if I'm to disconnect the filter drum from all the adjacent pipework.Thanks

At 5 years I would think you are due for a sand change. The sand doesn't need to harden up before it loses its efficiency. I usually suggest changing the sand every 3-4 years to avoid the sand hardening up in the filter and trashing the tank.

If you are backwashing with good flow, chances are you don't have any obstructions in the plumbing. I would suggest this - if your filter valve has a "recirculate" or a "pool/spa boost" setting, try running the pool on that setting. This will bypass the filter and just recirculate the pool. If your flow improves, then you know the pipes are not blocked. At that point I would go ahead and change the sand.

If you have to saw the pipes to get the filter tank out, you may want to consider buying a couple of unions and plumb those in while you have it apart. It will save the time & hassle of having to cut & couple everything back together if you ever need to pull the filter out again.